Change how replacements are filtered (#541)

This replaces the use of `isExpansionInMainFile` with instead taking the list of input files, and only touching them. This doesn't keep `isExpansionInMainFile` because it should be redundant, and as such it'd be easy to forget. Unless it starts being a performance issue, it's probably better to omit.

migrate_cpp/cpp_refactoring/main.cpp

@@ -9,11 +9,27 @@
 namespace cam = ::clang::ast_matchers;
 namespace ct = ::clang::tooling;
 
+// Initialize the files in replacements. Matcher will restrict replacements to
+// initialized files.
+static void InitReplacements(ct::RefactoringTool* tool) {
+  auto& files = tool->getFiles();
+  auto& repl = tool->getReplacements();
+  for (const auto& path : tool->getSourcePaths()) {
+    auto file = files.getFile(path);
+    if (file.getError()) {
+      llvm::report_fatal_error("Error accessing `" + path +
+                               "`: " + file.getError().message() + "\n");
+    }
+    repl.insert({files.getCanonicalName(*file).str(), {}});
+  }
+}
+
 auto main(int argc, const char** argv) -> int {
   llvm::cl::OptionCategory category("C++ refactoring options");
   auto parser = ct::CommonOptionsParser::create(argc, argv, category);
   ct::RefactoringTool tool(parser->getCompilations(),
                            parser->getSourcePathList());
+  InitReplacements(&tool);
 
   // Set up AST matcher callbacks.
   cam::MatchFinder finder;